Oddity in snd_uaudio(4) driver?

[Alexander Leidinger]

Quoting Ed Schouten <ed at fxq.nl> (from Thu, 7 Sep 2006 13:38:20 +0200):

CCing multimedia@, where all "the cool sound guys hang out"...

> Hello,
>
> I was just looking through FreeBSD's snd_uaudio(4) driver, because I'm
> thinking of patching it to support Xbox 360 headsets as well. I was
> looking at the code to set the sample rate in
> /sys/dev/sound/usb/uaudio.c. In that file there is the following code
> near line 4100:
>
> | 	if (speed >= UA_SAMP_LO(asf1d) && speed <= UA_SAMP_HI(asf1d)) {
> | 		ch->sample_rate = speed;
> | 		return speed;
> | 	} else if (speed < UA_SAMP_LO(asf1d)) {
> | 		score = 0xfff * speed / UA_SAMP_LO(asf1d);
> | 		if (score > hiscore) {
> | 			bestspeed = UA_SAMP_LO(asf1d);
> | 			hiscore = score;
> | 		}
> | 	} else if (speed < UA_SAMP_HI(asf1d)) {
> | 		score = 0xfff * UA_SAMP_HI(asf1d) / speed;
> | 		if (score > hiscore) {
> | 			bestspeed = UA_SAMP_HI(asf1d);
> | 			hiscore = score;
> | 		}
> | 	}
>
> If we would rewrite this code to something more basic, let's say we
> rename 'speed' to 'x' and the UA_SAMP_ macros to some predefined
> variables:
>
> | 	if (x >= 10 && x <= 20) {
> | 		...
> | 	} else if (x < 10) {
> | 		...
> | 	} else if (x < 20) {
> | 		...
> | 	}
>
> Wouldn't that mean that the last portion of the code is never reached?
> Looking at the code, it looks like some range check, making sure the
> sample rate remains inside a certain range. Wouldn't it be enough to
> remove the entire third if-statement, using a normal '} else {'?

Just by looking at the code you pasted, I assume the last part is a  
typo in the uaudio code and should be a '>' instead of a '<': "if it  
is outside the range, use the end of the range as a good candidate."

Bye,
Alexander.

-- 
The most delightful day after the one on which you buy a cottage in
the country is the one on which you resell it.
		-- J. Brecheux

http://www.Leidinger.net    Alexander @ Leidinger.net: PGP ID = B0063FE7
http://www.FreeBSD.org       netchild @ FreeBSD.org  : PGP ID = 72077137